An experimental treatment helps restore normal brain structure and function in mice that have sustained severe concussions, and could lead to a drug that would do the same in humans, according to new research.

The brains of people who suffer from chronic traumatic encephalopathy (CTE), a progressive neurodegenerative disease that affects people such as boxers and football players with a history of repetitive hard hits to the head, are characterized by fibrous tangles of a protein called tau. It is not known how traumatic brain injury leads to these tangles, which are also found in the brains of people who suffered from Alzheimer’s disease.

Now researchers say they have identified a precursor to the tangles—a misshapen form of tau that appears in the brains of mice shortly after a blow to the head—and have shown that it can be eliminated by a protein, called an antibody, that binds to the misshapen tau and marks it for destruction by the body’s mechanism for clearing damaged or unneeded proteins. In mice that have sustained severe traumatic brain injuries like those commonly sustained by soldiers after a blast or by athletes after a blow to the head, the treatment prevents neurodegeneration and helps restore normal function. This suggests that the misshapen tau is a “major early driver of disease” after traumatic brain injury, say the researchers, and represents a promising drug target. The research was funded by the National Football League Players Association, the National Institutes of Health, and the Alzheimer’s Association.

Though the brains of individuals who had CTE are full of tau tangles, until now it has not been clear whether this “tauopathy” is a cause or a consequence of the post-traumatic neurodegeneration, says Kun Ping Lu, a professor of medicine at Harvard Medical School, who led the new research. He says this result confirms that it is a cause.